An inflatable airbag system used in an automobile often must be able to maintain adequate internal gas pressure in its airbag over an extended period of time (on the order of seconds). This is particularly true in rollover applications, where protection provided by the airbag may be needed for a longer time.
Conventional airbag systems typically maintain pressure in the airbag by using a combination of a sealed airbag and a low-gas-temperature inflator (such as a stored gas device). A sealed airbag typically maintains pressure longer than other airbags, such as partially sealed airbags, unsealed airbags, and higher permeability airbags. A low-gas-temperature inflator is more conducive to maintaining pressure than inflators that generate and release higher temperature gases (such as hybrid and pyrotechnic inflators). The high-gas-temperature inflators produce relatively high temperature gas that will quickly cool while in the airbag. The gas will decrease in volume as it cools, and thus there will be less internal pressure in the airbag and the airbag will lose its fullness.
It is desirable to provide an airbag system that can readily maintain adequate internal gas pressure in its airbag. It is particularly desirable to provide such a system that can accommodate a variety of airbags (e.g., partially sealed airbags, unsealed airbags, and higher permeability airbags) and a variety of inflators (e.g., hybrid and pyrotechnic inflators).